This project attempts to develop novel molecules as allosteric anticoagulants of coagulation proteases, especially thrombin and factor XIa. The hypothesis is that targeting these proteases through allosteric disruption of their catalytic triad results in controlled inhibition, which is likely to not suffer from bleeding consequences. All current anticoagulants including the heparins, warfarin, dabigatran and rivaroxaban suffer from enhanced risk of bleeding. The past grant period resulted in two groups of highly promising inhibitors of thrombin and factor XIa. The thrombin inhibitors displayed regulatory features (maximal inhibition in the region of 50 - 75%), which is likely to maintain hemostasis, especially under prophylactic application. Likewise, factor XIa inhibitors are likely to be devoid of bleeding because of the inherent mechanism of action of factor XIa, which is its action on the thrombotic process while leaving hemostatic process intact. In addition, the allosteric inhibitors are predicted to possess a higher specificity of action, which would reduce off target effects. Thus, the two groups of inhibitors are predicted to lead to a safer anticoagulant therapy. In fact, we have found that one of our designed molecules showed marked anticoagulant activities in FeCl3-induced thrombosis in the carotid artery mouse model without affecting bleeding time supporting the hypothesis. In this grant period, we intend to I) design more potent, selective regulators of human thrombin; II) develop more potent, selective inhibitors of human factor XIa and III) perform pre-clinical studies on promising advanced thrombin regulators and FXIa inhibitors.